[Updated 9/15/2011] Although Microsoft CEO Steve Ballmer said Windows 8 would support both ARM and Intel processors on Wednesday and a parade of Microsoft execs portrayed Windows 8 PCs and tablets as equal citizens, Microsoft came clean late Wednesday and said Windows 8 on ARM-based systems will not ru Windows 7-and-earlier applications. Thus, only Metro-based apps are truly cross-device in Windows 8.

The new version, code-named Windows 8, is now in developer preview and will be available for download later today from dev.windows.com, with no release date yet set.

Sinofsky said Microsoft redesigned Windows because "things are a whole lot different now than three years ago.... Touch is a whole new dimension. Mobility is a whole new dimension.... We want Windows to respond to that." He also said Windows 8 uses just 281MB of RAM, down from 404MB in Windows 7, and that all the new capabilities are native to the core OS, not layered on top of it. That should ease development and aid performance, he said. Microsoft has said Windows 8 will not run on smartphones, which will use Windows Phone 7 instead.

Like Windows 7, Windows 8 is designed for touchscreen PCs where users gesture on their vertical monitor screens, a contrast to Apple's strategy of restricting gestures to horizontal touch surfaces such as a touchpad. (Non-touchscreen PCs use traditional pointing devices instead, as do non-touch-savvy apps.) It also runs on iPad-style tablets. Thus, Windows 8 includes APIs for mobile devices' sensors, such as accelerometer, near-field communications, and device orientation. There are also new APIs to simplify integration of Wi-Fi and 3G networking and of printing, as well as to integrate storage, setup, and sharing access via Microsoft's Windows Live cloud service.

The new Start screen is no longer just an icon launcher, but now is a series of tiles that can contain live data, application screens, communications screens, and more. When clicked or tapped, the tile opens the content or app in its own window. Apps can interact through common exchange APIs, in what Sinofsky called a "web of apps." The Windows Explorer interface had also been tweaked, such as to allow use of custom icons in the toolbar.

Windows 8 adopts several capabilities pioneered by Apple in Mac OS X, including full-screen apps, app autosave (required for Metro apps), OS-wide search, and OS-wide spell-checking. Microsoft is also working on an HTML5-savvy version of Internet Explorer. IE is the only remaining major browser that's not HTML5-savvy.

For developers, Microsoft has exposed its new WinRT APIs so that you can access them from the language of your choice (including C#, XAML, and HTML5), rather than have the Visual Studio IDE restrict your language choice. A UI tool based on a proposed HTML5 grid standard helps developers design their apps visually to work on multiple screen sizes and orientations. Another tool helps developers port Win32s apps from Windows 7 to Windows 8's Metro style. Microsoft also will introduce an app store similar to Apple's Mac App Store, exceptit also lets customers try software before buying.

Sinofsky demonstrated a greatly simplified Windows update and restore capability, in which you can reset Windows to its original configuration without losing your music, photos, and videos -- as happens in previous versions of Windows. For power users, the system's activity monitor is greatly simplified yet enhanced with live graphical charting. Remoting has also been simplified. And when using multiple monitors, you can manage what appears on each display, similar to the Spaces feature in Mac OS X.

New to the Windows 8 client OS is inclusion of Hyper-V virtualization, which comes with a management tool for local VMs.

Microsoft has also revised its hardware specifications so new PCs can boot faster, better support solid-state drives, support disks as large as 256TB, reduce power usage through real-time component management (similar to how mobile phones work), and support touchscreens. Microsoft's specs also enable automatic use of graphics processors, something Apple introduced in Mac OS X Snow Leopard. The new spec also requires devices to have an embedded HD camera for videoconferencing.

InfoWorld executive editor Galen Gruman analyzes the latest issues in mobile technology and the consumerization of IT. He has also written or co-written more than 40 how-to books, on iOS, iPad, Windows 8, OS X, and desktop publishing.